In a solution polymerization process polymer is soluble in the hydrocarbyl solvent/diluent used for the process. At some locations or times in the process the polymer may come out of solution and the resulting polymer is generally difficult to re-dissolve in the solvent/diluent in the process. This polymer may have a different, typically higher, molecular weight and when the polymer is recovered from the process the gels tend to be separate resin particulates dispersed with in the main resin product.
There are a number of methods used to detect particles in a polymer. For example there are instruments to determine particle size distribution of or within a polymer sample. For example laser light scattering measurements are used in commercial equipment such as the Coulter™ LS230 or the Horeiba™ LA 910 particle size determination equipment. Generally these devices are used off line and the product is diluted in a solvent or diluent. Typically the procedure is conducted off line and it takes about 20 to 30 minutes to get the results. While the method is good for determining for example the particle size distribution within a latex or the size of rubber particles in a sample of high impact polystyrene resin the process is not suitable for in or on-line real time measurement during a polymerization.
U.S. Pat. No. 5,151,474 issued Sep. 29, 1992 to Lang et al., assigned to the Dow Chemicals Company teaches an on-line real time process to monitor the concentration of monomer and co monomer in a recycle stream during a solution polymerization process using Fourier transform infrared spectroscopy (FTIR). The patent fails to suggest the method could be used to detect gel flurries in the process. Further the process of the reference adsorption peaks are measured at specific wavelengths and not over the entire spectra.
U.S. Pat. No. 6,072,576 issued Jun. 6, 2000 in the name of McDonald et al., assigned to Exxon Chemical Patents Inc. teaches a process to control a number of reactions including polymerization in which a Fourier transform near infrared (FTNIR) spectra is used to control such a reaction to produce a product having a desired set of properties. A standard set of spectra for the desired product are obtained. The spectra are corrected for measurement errors (calibration curves). The corrected spectra are then weighted relative to an orthonormal base function. Then a value is obtained for each property of the calibration curves. Then determining a predictive model relating the value for the desired property to the set of weights (e.g. relating the spectra to the orthonormal base function). Then a spectra is obtained and an estimated value for the property is determined from the spectra and the difference between the value of the property and the value of the estimate is used to control the process (to return the value of the estimate to the value of the property). The present invention does not contemplate such a process. Rather it indirectly (via noise) measures the presence of gels in the solution of polymer in the process.
The present invention seeks to provide a simple in-line or on-line method to determine the presence of gel flurries in a solution polymerization process.